The present invention relates to the field of printed circuit boards. More particularly, this invention relates to an assembly process of a chip, such as a microprocessor chip, and heat sink to a circuit board.
Some present assembly processes and heat sink designs may use thermal grease between the heat sink and the chip to improve thermal conductivity. Typically, thermal grease is applied between the chip and heat sink and the chip is attached to the circuit board. The thermal grease forms a thermal as well as mechanical bond between the chip and the heat sink which provides good heat transfer characteristics, but complicates replacement of the chip. Field replacement of the chip is difficult because thermal grease is difficult to work with and is not forgiving. The dispensing and application process must be precise for the interface to function properly. Therefore, field application of thermal grease is generally not feasible.
Therefore, in order to replace the chip, the chip and heat sink must be assembled in the factory and sent out as a unit to the field for installation. In order for the unit to be reliably installed in the field, coarse and fine alignment features are needed between the chip and the circuit board, between the chip and the heat sink and between the heat sink and the circuit board. These alignment features add cost and make it difficult to separate the chip from the heat sink for reuse of the heat sink.
What is needed is an assembly process and heat sink design that reduces the number of alignment features and allows for field replacement of the chip.
The present invention includes one embodiment of a printed circuit board assembly including a printed circuit board, a microprocessor chip, a socket and an actuator for connecting the chip to the printed circuit board, a heat sink for attachment to the top surface of the chip, and a thermal interface pad positioned between the heat sink and the microprocessor chip. The heat sink has an actuator access opening so that the actuator is operable with the heat sink positioned on top of the microprocessor. Optionally, the thermal interface pad is field installable. Optionally, the thermal interface pad includes a phase change material. Optionally, the connection between the chip and the heat sink is free of fine or all alignment features so that they may be separated by twisting the heat sink relative to the chip. Optionally, the connection between the heat sink and the circuit board is free of fine or all alignment features to reduce cost.
One embodiment includes a method of assembling a printed circuit board assembly including attaching a socket and actuator to the printed circuit board, positioning a microprocessor chip on the socket, actuating the actuator to secure the chip to the printed circuit board, positioning a thermal interface pad on the top surface of the chip, positioning a heat sink on the top surface of the thermal interface pad, and securing the heat sink to the printed circuit board.
Optionally, positioning the microprocessor chip on the socket is positioned without fine or all alignment features or positioned by hand.
One embodiment includes a method of disassembling and re-assembling a printed circuit board assembly including actuating an actuator of a socket attached to a printed circuit board with the socket securing a first chip to the printed circuit board and the first chip having a first thermal interface pad and a heat sink secured to the chip, removing the first chip and heat sink from the socket, separating the first chip from the heat sink, disposing the first chip and the first thermal interface pad, positioning a second chip on the socket, actuating the actuator to secure the second chip to the printed circuit board, positioning a second thermal interface pad on the top surface of the second chip, positioning the heat sink on the top surface of the second thermal interface pad, and securing the heat sink to the printed circuit board.
Optionally, positioning the second chip on the socket is positioned without fine or all alignment features.
Optionally, at least part of or all of the method is conducted in the field.